1. Field of the Invention
The present invention relates to a synthetic metal working liquid, concentrate thereof, and method for mechanically working cobalt-containing metals. The concentrate is suitable, after dilution with water to provide the synthetic metal working liquid, for use in the mechanical working method. The method is carried out with the synthetic metal working liquid which is comprised of specific tertiary amines which are alkanol amines capable of reducing both the release of cobalt ions and the corrosion of iron.
2. Discussion of the Art
The mechanical working of hard metals, i.e., cemented carbides containing cobalt, by, for example, grinding the cobalt-containing hard metals, is usually carried out in the presence of a metal working liquid also known as an aqueous cooling lubricant. The aqueous cooling lubricant contains a lubricant, such as a fatty acid salt, and frequently contains iron corrosion inhibitors, such as salts of triethanol amine. During mechanical working, a large quantity of chips are produced having a large surface area which, when exposed to the aqueous cooling lubricant, participate in corrosion processes, whereby the content of ionic cobalt in solution in the aqueous cooling lubricant will reach high levels. Frequently, the cobalt concentration amounts to several hundreds of milligrams per liter of cooling lubricant.
Besides the negative effect which the corrosion processes have on the appearance and dimensional tolerances of the metal surface, ionic cobalt constitutes a serious health hazard to human beings who come into contact therewith by touch or via airborne aerosol. Ionic cobalt is a strong allergen for man. One way of reducing the content of ionic cobalt in recirculating cooling systems is to filter the cooling lubricant; another way is to make frequent changes of cooling lubricant, simultaneously as tanks and machines are thoroughly cleaned.
U.S. Pat. No. 4,315,889 to J. M. McChesney et al. describes a method of reducing leaching of cobalt from metal working tools containing tungsten carbide particles bonded by cobalt. According to this Patent, metal working is carried out in the presence of metal working compositions containing, as the active component, a specific triazole or thiadiazole compound. The compositions may be water-based, oil-in-water emulsions or oil-based. The aqueous coolant and lubricant metal working composition further comprises boric acid, an amine or mixture of amines, sodium gluconate, and an aromatic or paraffinic carboxylic acid. The amine or mixture of amines react with the boric acid and organic carboxylic acid components of the composition to form salts. The amine component can be a secondary or tertiary amine with sufficient reactivity, such as di- or triethanolamine, triisopropanol amine and 2-dimethylamino, 2-methyl, 1-propanol amine.
U.S. Pat. No. 3,280,029 to H. F. Waldmann describes a lubricant composition for reducing vapor phase corrosion and metal fatigue. Certain secondary or tertiary amines which are alkyl amino monoalkanols are incorporated into the lubricant and have the general formula ##STR1## where R represents an alkyl group, R.sup.1 represents an alkyl group the same or different from R, or a hydrogen atom, R and R.sup.1 are selected so that the sum of the groups represented by R+R.sup.1 does not exceed 10 carbon atoms, X is an alkylene group having from 2 to about 4 carbon atoms, and n is 1 or 2. The lubricant composition may be a lubricating oil or a water-in-oil emulsion having from 10 to 70% by weight of water. The alkyl amino monoalkanols must be present in an effective state so that they are free to act in the lubricant composition, that is, they should not be tied up as reaction products with other components.